The present invention relates to a novel method for removing halogens such as fluorine and chlorine in olefin compounds using inorganic solid agent containing aluminum atoms. The halogen is contained as trace residual impurities in the olefin compounds in the forms of organic compounds, inorganic compounds or mixtures of them. Furthermore, the method of the present invention is characterized in that the isomerization of non-conjugated carbon-carbon double bonds in the olefin compounds can be suppressed substantially. Especially, even in the removal treatment done for a long period time, the present invention provides a method to suppress the above-mentioned isomerization substantially. Still further, the present invention relates to a method for producing highly reactive butene oligomers, in which the above method is applied to butene oligomers that is obtained by polymerization of butenes, thereby effectively reducing the content of terminal fluorinated groups formed at terminals of oligomers, in addition, converting the terminal fluorinated groups into useful terminal vinylidene groups which are highly reactive.
Butene oligomers having regular repeating structural units and vinylidene structures at their terminals of molecules are good in thermal decomposition property owing to the regularity of the repeating structural units and the uniformity in the distribution of terminal groups having a specific structure. Furthermore, they can react with maleic acid or the like in high yield. Polybutenyl succinic anhydride obtained by this reaction is further modified with amines into compounds, which are used industrially on a large scale because of their usefulness as additives for lubricant oils or fuel oils.
The useful butene oligomers as referred to in the foregoing passage are produced by polymerizing butenes such as isobutene in the presence of boron trifluoride catalyst (e.g., U.S. Pat. Nos. 4,152,499 and 4,605,808). Another method for producing butene polymers using aluminum chloride complex catalyst containing an organic nitro-compound as complexing agent is disclosed in U.S. Pat. No. 5,012,030.
However, among the butene oligomers produced through these methods, fluorine atoms, for example, derived from the boron trifluoride catalyst often remain as much as about 200 ppm (by weight). When the butene oligomers are converted into additives for lubricant oils or fuel oils or thus converted fuel oil additives are burned in running engines, the residual fluorine is decomposed into hydrogen fluoride, which may cause the corrosion of apparatus and the pollution of environment.
When polymerization is carried out using pure isobutene as a starting material and boron trifluoride as catalyst, it is possible to produce butene oligomer of the content of residual fluorine as low as 1 to 10 ppm as fluorine atom, by adjusting the molar ratio of boron trifluoride in catalyst and the complexing agent. However, the use of pure isobutene is costly and it is not advantageous in view of industrial practice. Moreover, it is necessary to carry out certain operations for dehalogenation in order to obtain a substantially halogen-free products.
On the other hand, when inexpensive butadiene raffinate can be obtained as a starting material in practical working, the formation of the residual fluorine originating from catalysts cannot be avoided, as long as boron trifluoride is used as catalyst. Furthermore, when a post-treatment is adopted for removing the residual fluorine, it causes a problem that the features of butene oligomer such as the regularity of the repeating structural units and the uniform presence of specific terminal groups are destroyed. By the way, when isobutene or butadiene raffinate is polymerized by using catalysts of aluminum chloride or its complex, chlorine sometimes remains and causes the same problem as in the case of boron trifluoride complex catalysts containing alcohols as complexing agents.
For example, in Japanese Laid-Open Publication No. S57-183726 (corresponding to U.S. Pat. No. 4,417,091), it is proposed that a butene fraction is polymerized into oligomer with a fluorine-containing nickel catalyst and the fluorine contained in the obtained olefin trimer is removed by the treatment with silica gel, for example. However, as shown in comparative examples later, in the case of polymers obtained by polymerizing C4 fractions using boron trifluoride as catalyst, the treatment with silica gel cannot remove fluorine sufficiently.
As a further problem, it is sometimes noticed that double bonds in polymer are isomerized during the treatment so that the high content of terminal vinylidene group formed by polymerization is reduced. Incidentally, each isomerization (transfer) of carbon-carbon double bond in polymer is a kind of chemical reaction, and is sometimes accelerated with specific catalyst respectively.
The present inventors found out that they could accomplish dehalogenation while preventing double bonds from isomerizing by bringing polymers into contact with inorganic solid agent containing aluminum atoms.
As the result of further study by the present inventors, the following has become clear concerning the butene polymer that has been obtained according to the description of U.S. Pat. No. 4,605,808 mentioned above. When the butene polymer having a high content of terminal vinylidene structure and containing several ten to several hundred ppm of fluorine as organic fluorine impurity is brought into contact with alumna, isomerization of terminal vinylidene structure as a side reaction shown in the next formula is caused to occur remarkably as the treatment continues. After all, the content of terminal vinylidene structure is reduced by the treatment with alumina in a long period of operation.
xe2x80x83(CH3)3C[CH2C(CH3)2]nCH2C(CH3)xe2x95x90CH2xe2x86x92(CH3)C[CH2C(CH3)2]nCHxe2x95x90C(CH3)2
When butene polymers separately produced and containing no fluorine compound are treated with alumina, the above isomerization can be hardly recognized. Therefore, the phenomenon that the content of terminal vinylidene structure is reduced cannot be attributed to the effect by alumina itself of accelerating isomerization.
In the above example, the removal of fluorine compound contained in the butene polymer having a high content of terminal vinylidene structure is explained. However, as to unreacted C4 fraction remaining after polymerization of butadiene raffinate with fluorine-containing catalyst, there is the same problem.
Because the above unreacted C4 fraction is usually burned as a fuel intact or after 1-butene useful as a co-monomer for adjusting the density of high density polyethylene has been separated and removed, the concentration of the residual fluorine makes a problem for the same reason as in the case of butene polymer. In this case, dehalogenating treatment with an inorganic solid agent containing aluminum atoms is also useful and economic. However, 1-butene is likely to be isomerized to 2-butene in the similar manner to that shown in the above formula. When unreacted C4 fraction in particular is used as a source of supply of 1-butene, it is important to suppress the isomerization of 1-butene to 2-butene.
When the present inventors investigated the above phenomenon of isomerization energetically, they have found out that fluorine fixed on alumina generates new acidic sites in addition to those inherent in alumina so that the isomerizability of alumina itself changes and the isomerization is accelerated.
In other words, it is supposed that fluorine atoms fixed on alumina form new strong Lewis acidic sites there, and the newly formed strong Lewis acidic sites accelerate the isomerization of non-conjugated carbon-carbon double bonds on the occasion of contact treatment for defluorination. The above-mentioned isomerizability increases with the total amount of the fluorine removed by defluorinating treatment, that is, the fluorine fixed on alumina by defluorinating treatment.
For example, in Japanese Patent Publication No. H06-28725 (corresponding to U.S. Pat. No. 5,288,849), it is proposed that olefins are refined with alumina compounds impregnated with alkali or alkali earth metals. That is, it is disclosed that the isomerization of olefins can be suppressed by impregnating alumina with alkali or alkaline earth metals.
However, by the method of adding alkali or alkaline earth metal proposed in the above patent, it is noticed that the ability of removing halogen such as fluorine rather decreases unfavorably. Moreover, there is a more important problem.
When the above-mentioned method proposed in Japanese Patent Publication No. H06-28725, wherein alumina is previously impregnated with a fixed amount of alkali metal or the like so as to keep the isomerizability low, the amount of alkali metal or the like is not sufficient to neutralize the strong acidic sites of Lewis acids which are newly generated by the treatment, even though defluorination is possible. As a result, isomerization of carbon-carbon double bonds begins to take place gradually according to the total amount of the fluorine removed in excess of a certain amount. However, when alumina is impregnated previously with a large excess of alkali or alkaline earth metals, the ability of removing halogen rather decreases owing to a bad effect caused by the excess of alkali.
As mentioned above, in the case of the alumina which is previously impregnated with alkali metal or the like as proposed in the above Japanese Patent Publication No. H06-28725, the removal of fluorine is insufficient, and moreover, the duration period is markedly short even though removal is possible, which is a fatal problem.
The object of the present invention, that is, the suppression of the isomerizability by alumina, is attained by neutralizing selectively the strong Lewis acidic sites which are newly generated by a treatment of defluorination to weaken or make harmless the isomerizability.
An aspect of the present invention is to provide a method of increasing the content of terminal vinylidene group rather than decreasing it and leaving no fluorine substantially, when highly reactive butene oligomers are produced with boron trifluoride type complex catalyst using commercially and cheaply available butadiene raffinate as a starting material.
Another aspect of the present invention is to provide a method of carrying out a contact treatment while suppressing the isomerization of the above carbon-carbon double bonds which is caused by the strong Lewis acidic sites newly generated during the process of defluorination, when organic compounds are brought into contact with an alumina-containing inorganic solid agent in order to reduce the concentration of residual fluorine in the organic compounds containing halogen compounds such as fluorine compound as impurity and having at least one non-conjugated carbon-carbon double bond in the structure.
A further aspect is to provide a method of reducing selectively the increased isomerizability of alumina, which still has the ability of defluorination, and reusing the alumina for the contact treatment,.
A still further aspect of the present invention is to provide the polybutene having the content of the terminal vinylidene structure maintained at 60% or more of the content before the treatment and having the fluorine remaining in a polymer reduced as far as practically harmless, by polymerizing a starting material of C4 using boron trifluoride as a catalyst and feeding the obtained polymer having the high content of terminal vinylidene structure into a post-treatment step.